This invention is directed to silicone copolymers prepared by nonaqueous interfacial polymerization, where polycondensation takes place at the interface between reactive starting materials dissolved in separate and immiscible solvents. One example is an alternating polysiloxane copolymer of dimethyl and diphenyl siloxanes obtained by the condensation of a phenyldichlorosilane with an alkali metal methyl silanolate. A major advantage of interfacial polymerization of silicon containing monomers is ability to control structures of resulting polymer chains and compositions of copolymers, without need of a conventional catalyst, and without problems associated with rearrangement during polymerization.
Interfacial polymerization of certain organic monomers is a known polycondensation reaction wherein monomers are dissolved in immiscible solvents. Polymerization occurs when the monomer in one phase diffuses from the bulk of the solution into the interface and reacts with the monomer from the other phase. The polymerization rate depends on diffusion rates and reactivity of functional groups on the monomers.
We have found that when a dichlorosilane is dissolved in one phase, and a potassium silanolate or other metal silanolate, is dissolved in the other phase, the reaction rate to form potassium chloride or other chloride salt is faster, compared to the typical polycondensation reaction, and leads to high molecular weight polysiloxanes.
Furthermore, since the inorganic salt by-product is not soluble in either of the organic solvents, it precipitates and does not interfere with the polycondensation reaction. If the copolymer is insoluble in either solvent, it also precipitates and can be removed from the interface.
Among some known interfacial polymerization reactions are polycondensation of amines with acetyl chloride to form nylon (i.e., polyamides), and the reaction of alcohols with acids to form polyesters. Interfacial polymerization of these organic monomers typically provide faster polymerization rates than other types of polymerization reactions such as bulk or solution polymerizations. Even more important is the fact that higher molecular weight polymers can be obtained because stoichiometry between the monomers need not be precise.
This is particularly critical for organic polycondensation reactions where an imbalance of a fraction of a percent causes the extent of polymerization to be greatly affected. Another advantage of interfacial polymerization reactions is formation of high molecular weights at the interface regardless of overall percent conversion of bulk amounts of the two reactants still in solution.
Thus, among the many advantages offered by interfacial polymerization in synthesis of various organic polymers are (i) the ability to prepare infusible polymers; (ii) the ability to synthesize polymers with chemically active substituents as well as heteroatoms; (iii) controlled crosslinking of polymer structure; (iv) the ability to use cis- and trans-conformation without rearrangement; (v) the ability to prepare optically active polymers without decomposition of intermediates; (vi) the ability to use short-chain and ortho-substituted ring intermediates; (vii) the ability to use thermally unstable intermediates to form thermally stable polymers; (viii) the ability to form block and ordered copolymers; (ix) the ability to form synthetic elastomers; (x) a direct method of forming polymer solutions and dispersions; (xi) a direct method for polymerization of polymer coatings; and (xii) a direct method for polymerization of monomers to fibrous particulates, fibers, and films.
We have now discovered that many of these advantages can be utilized in the interfacial polymerization of silicon containing monomers to form siloxane polymers and copolymers.